Upgrade notice for ArbOS 61
ArbOS 61 "Elara" is active on Arbitrum Sepolia, Arbitrum One, and Arbitrum Nova. It activated on Arbitrum One and Arbitrum Nova on Thursday, August 20, 2026.
If you run a node on these chains, you must run Nitro v3.11.3 or higher to sync.
- Docker image: offchainlabs/nitro-node:v3.11.3-beb2108
- Release notes: https://github.com/OffchainLabs/nitro/releases/tag/v3.11.3
- WASM module root:
0xc10cd7ec6acaf1c441a3f6bd0900ad20f15855ba775a96f1939118cbc629dc97(consensus-v61)
Actions required for node operators
Sepolia network
ArbOS 61 activated on the Arbitrum Sepolia chain on Monday, June 29, 2026, at 15:00 UTC.
Arbitrum One and Arbitrum Nova
The ArbitrumDAO approved ArbOS 61 for Arbitrum One and Arbitrum Nova in a Constitutional onchain vote. After the waiting periods and phases set out in the ArbitrumDAO Constitution, ArbOS 61 activated on both chains on Thursday, August 20, 2026.
The Arbitrum DAO network upgrades table records the exact activation time of each chain.
Important dates
The following dates are relevant for Arbitrum chain operators.
| Date | Network upgrade | Affected audience |
|---|---|---|
| Monday, June 29, 2026 at 15:00 UTC | Arbitrum Sepolia upgrade to ArbOS 61 | Node operators running Arbitrum Sepolia |
| Thursday, August 20, 2026 at 17:00 UTC | Arbitrum One/Nova upgrade to ArbOS 61 | Node operators running Arbitrum One/Nova |
Actions for Arbitrum chain owners
ArbOS 61 has run on Arbitrum One for more than 30 days. You can upgrade your Arbitrum chain now.
To upgrade, follow How to upgrade ArbOS on your Arbitrum chain and the nitro-contracts upgrade instructions. Use the Nitro version, Docker image, and WASM module root listed above.
ArbOS 61 lets your chain collect priority fees. Do not enable Priority Gas Auctions (PGA) or priority fee collection on your chain yet. Offchain Labs updates this notice when chain operators can enable them.
Do not call setMultiGasPricingConstraints on the ArbOwner precompile. ArbOS 61 ships multi-dimensional gas pricing in the node software, but a future Nitro version removes it. If your chain has it enabled when that version ships, your chain forks.
You can now use multi-constraint pricing with a single gas dimension. To configure it, call setGasPricingConstraints as described in Dynamic Pricing for Arbitrum chains.
Context
ArbOS 61 "Elara" builds upon ArbOS 51 "Dia". It makes two changes to Arbitrum One and Nova: it raises the Stylus contract code size limit to 96 KB, and it adds a BaseFeeManager contract that manages the minimum L2 base fee.
ArbOS 61 also ships three optional features. A chain owner must enable each one explicitly:
- Alternative Data Availability (AltDA) Layer API. Disabled on Arbitrum One and Nova. It requires nitro-contracts v3.2.0 or higher. To learn how to build a custom DA provider against the new API, refer to How to integrate with the DA API.
- Compliance transaction filtering. Disabled on Arbitrum One and Nova. On a live chain, filtering takes effect seven days after the chain owner enables it. To learn how transaction filtering works, refer to Compliance filtering.
- Priority fee collection. Enabled on Arbitrum One since September 23, 2026, together with PGA. Disabled on Nova. To learn how to enable it, refer to Priority fee collection.
ArbOS 61 corrects two interacting bugs in the gas refund logic that were found while testing ArbOS 60 on Arbitrum Sepolia. The fixes change the State Transition Function (STF), so they required a new ArbOS version. ArbOS 60 never activated on Arbitrum One or Nova, so neither chain was affected.
ArbOS 61 passed a Snapshot temperature check and then a Constitutional onchain vote, which closed on August 1, 2026. To learn more about the proposal, refer to the ArbOS 61 Elara AIP.